You can change or remove column defaults using the same form of the ALTER TABLE statement you use to create defaults. The following statement changes the default value of a column named order_date from its current setting to CURRENT DATE:
ALTER TABLE sales_order MODIFY order_date DEFAULT CURRENT DATE
You can remove column defaults by modifying them to be NULL. The following statement removes the default from the order_date column:
ALTER TABLE sales_order MODIFY order_date DEFAULT NULL
